Inductance coil structure



sept- 1951 R. E. WHIFFEN 2,568,310

' INDUCTANCE con, STRUCTURE Filed March 30, 1948 QYWM'VM RICHARD E. WHIFFEN gwam Patented Sept. 18, 1951 INDUCTANCE COIL STRUCTURE Richard E. Whiflen, Towson, Md., asaignor to Bendix Aviation Corporation, Towson, Md a corporation of Delaware Application March 30, 1948. Serial No. 18,042

4 Claims. I

This invention relates to inductance coils and particularly to such coils as employed in high frequency radio circuits.

It has been known to tune coils of this type by providing a core of finely powdered iron embedded in a binder and molded into cylindrical shape. The coils have been wound on cylindrical forms of paper or other material of this nature and the powdered iron cores have sometimes had their peripheral surfaces formed into screw threads cooperating with similar threads formed on the interior of the coil form. Tuning was then accomplished by screwing the core into or out of the form.

In order to prevent unwanted coupling between the magnetic field of the coil and the magnetic fields of other components of radio apparatus in which the coil is used, it has been necessary to provide shields of magnetic material completeLv surrounding the coils. These have been bulky, thus preventing compact arrangement of components and have added to fabricating time and expense.

It is an object of this invention to provide a coil structure which is of compact construction.

It is another object of the invention to provide a coil having maximum possible Q and undergoing a minimum loss of Q when the coil is mounted in a very confined space such as an intermediate frequency transformer.

It is a further object to provide a coil which lends itself to mass production methods by requiring fewer component parts and fewer operations in its construction.

It is another object to provide a structure in which each turn of the coil is substantially completely surrounded by a low reluctance path whereby leakage between turns is reduced to a minimum, the Q of the coil and the ratio of maximum to minimum inductance thus being maintained at high values.

It is a still further object to provide a coil structure in which the coil form surrounds the coil with a low reluctance path which minimizes the electromagnetic field external to the coil.

It is another object to provide an integrated coil assembly that is easily mounted.

The foregoing objects are all accomplished by a structure in which the coil is formed around the inner periphery of the bore of a hollow cylindrical body of powdered iron material, and a retractable core of powdered iron material is positioned in the bore, the bore having substantially the diameter of the bore.

In the drawings:

Fig. 1 is an elevational view in perspective of a core formed in accordance with the invention;

Fi 2 is a cross-sectional view of a coil structure formed in accordance with the invention, the section being taken along the longitudinal axis of the coil;

Fig. 3 is an elevational view, partly in section, of the coil structure of Fig. 2 with the core of Fig. 1 partially screwed into it; and

Fig. 4 is a cross-sectional view of a coil structure and core comprising a second embodiment of the invention, the section being taken along the axis of the form.

Referring now more particularly to the drawing, there is shown in Fig. 2 a hollow cylindrical body I of non-conductive powdered iron ma terial closed at one end. Wound around the inner periphery of the body I is a coil 2. The turns of the cOil are partially embedded in the material of the body I which thus acts as a coil supporting form. Since the turns are only partially embedded the portion of the coil which protrudes from the material of the form has the effect of forming a screw thread upon the inner periphery thereof. The ends of the coil are taken out through the side of the coil form as shown.

The core 3, as shown in Fig. 1, is a cylindrical mass of non-conductive, powdered iron material shaped to fit easily but snugly into the bore of the coil form and having formed in its lateral surface a spiral groove 4 conforming to the portion of the coil 2 protruding from the inner surface of the form. One end of the core is formed with a slot 5 to accommodate a screw driver or similar tool.

The assembled structure is shown in Fig. 3. A mounting base i of desired configuration may be formed in the closed end of the coil form.

A second embodiment of the invention is shown in Fig. 4 in which the core 3 is not provided with a spiral groove. In this form of the invention the coil 2 is almost compeltely embedded in the material of the form, only a small portion of its inner peripheral surface being exposed to the core. B this means, the flux path around the wire of each turn is still composed almost entirely of magnetic material, the air-gap being very small. Conventional methods of varying the insertion of the core may be used.

Coil structures embodying the invention lend themselves to several methods of construction. One suggested method involves the use of a mandrel of the diameter of the desired bore of the coil form. The mandrel is formed with a accamo in a cavity mold which is then closed off. Powdered iron of the proper physical characteristics suspended in a suitable non-conductive casting vehicle is next injected into the cavity. The mold is then suitably partially cured. The molded coil is removed and further cured after which it is ready for use.

The core may be constructed by casting a solid slug of powdered iron and machining it to the desired configuration. A preferred method, however, involves molding the core in a mold formed to the proper configuration to produce a core of the desired dimensions and form. The non-conductive powdered iron material of the form and the core is known to the art.

The powdered iron external to the winding is of but incremental assistance in producing a higher coil Q. It is of considerable use, however, in confining the magnetic field of the coil, providing in conjunction with the core a low reluctance path for the coil flux. This low reluctance path completely surrounds the coil and thus minimizes the external field. It will be seen that the wires of the coil turns are almost completely and vary closely surrounded with the magnetic material with the result that the air gap is greatly reduced over previous structures with an accompanying decrease in the reluctance of the flux path and minimizing of the coil leakage.

One of the virtues of the invention is the high Q of the coil and the high ratio of maximum to minimum inductance made possible by the fact that each turn of the coil is almost completely surrounded with magnetic material, since in both embodiments the air gap in the flux path around the wire is very short.

Link coupled coils may be formed by winding a link coil of a suitable number of turns coaxially with the main winding.

What is claimed is:

l. A high frequency inductance device comprising a coil supporting form of non-conductive magnetic material, said form being provided with a cylindrical bore, a coil formed in the lateral surface of said bore, said coil being immovable with respect to said form, said coil constituting a screw thread on the inner surface of said form, and a cylindrical core of non-conductive magnetic material having substantially the diameter of said bore and having formed in its lateral surface a groove dimensioned to act as a screw thread co-acting with the screw thread formed by said coil to accurately position said core in said form.

2. A high frequency inductance device comprising a coil supporting form of non-conductive magnetic material said form being provided with a cylindrical bore, a coil formed in the lateral surface of said bore, said coil being integral with respect to said form, whereby said coil constitutes '4 a screw thread on the inner surface of said form,

and a cylindrical core of non-conductlve magnetic material having substantially the diameter of said bore and having formed in itslaterafsuri'ace a groove dimensioned to act as a screw thread coacting with the screw thread formed by said coil to accurately pwition said core in said form.

3. Ahigh frequency inductance device comprising a coil supporting form of non-conductive magnetic material, said form being provided with a cylindrical bore, a coil formed in the lateral surface of said bore, the wire of said coil being partially and uniformly embedded in the material of said form and Partially protruding therefrom, whereby, said coil constitutes a screw thread on the inner surface of said form, and a cylindrical core of non-conductive magnetic material having substantially the diameter of said bore and having formed in its lateral surface a groove dimensioned to act as a screw thread co-acting with the screw thread formed by said coil to accurately position said core in said form.

4. A high frequency inductance device comprising a coil supporting .form of non-conductive magnetic material, said form being of cylindrical shape and being provided with an axial cylindrical bore, a coil formed in the lateral surface of said bore, the wire of said coil being partially and uniformly embedded in the material of said form and partially protruding therefrom, whereby, said coil constitutes a screw thread on the inner surface of said form, and a cylindrical core of non-conductive magnetic material having substantially the diameter of said bore and having formed in its lateral surface of a groove dimensioned to act as a screw thread co-acting with the screw thread formed by said coil to accurately position said core in said form.

RICHARD E. WHIE'FEN.

REFERENCES CITED The following references are of record in the like of this patent:

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